1. Field of the Invention
The present invention relates to a semiconductor accelerometer, and more specifically to a semiconductor type accelerometer having a construction which offsets the detrimental effects of thermal properties.
2. Description of Related Art
One typical example of conventional semiconductor accelerometers has included a cantilever composed of a beam portion and a weight portion which are formed by etching a semiconductor substrate, for example, a silicon substrate. In addition, for example, four gauges are formed in the beam portion of the cantilever, so as to able to form a Wheatstone bridge. Each of the four gauges constitutes of a diffusion resistor formed by diffusing impurities into the silicon substrate.
The four gauges resistors (diffusion resistors) are interconnected by wiring conductors, which are formed of for example aluminum on the silicon substrate, so as to form the Wheatstone bridge. Each of four connection nodes of the Wheatstone bridge is connected through wiring conductors, which are also formed on the silicon substrate, to a corresponding one of four external connection pads.
With the above mentioned arrangement, if the semiconductor accelerometer is subjected to any acceleration, the cantilever, particularly the beam portion of the cantilever, is deflected, so that the Wheatstone bridge becomes unbalanced. Because of this imbalance, an output in proportion to the acceleration can be obtained by the Wheatstone bridge formed of the four gauge resistors.
In the above mentioned conventional semiconductor accelerometer, the four gauge diffusion resistors are interconnected so as to form the Wheatstone bridge as mentioned above. Here, assuming that the resistance of each diffusion resistor is R, and a contact resistance between each end of each diffusion resistor and an associated wiring conductor is .DELTA.R.sub.3, a gauge resistance GR.sub.2 for each one gauge resistor can be expressed: EQU GR.sub.2 =R+.DELTA.R.sub.3 .times.2
In the above mentioned conventional semiconductor accelerometer, however, the contact resistance is large and has a large variation or scatter, since the diffusion resistor is directly connected to the wiring conductor. As a result, an offset value of the Wheatstone bridge composed of the four gauge resistors significantly varies from one semiconductor accelerometer to another.
In addition, since the diffusion resistance and the contact resistance are different from each other in thermal properties, namely in a temperature coefficient of resistance, the temperature characteristics of the offset of the Wheatstone bridge has a significant variation from one semiconductor accelerometer to another.